Classically, internal combustion engines are equipped with a turbocharger having a turbine driven by the energy of the exhaust gas and a compressor integrally coupled to the turbine. At a low engine speed rotation the turbocharger is assisted by an electrical machine.
As illustrated in U.S. Pat. No. 4,769,993, one way to provide electrical support for turbocharging is to integrate an electric motor into the turbocharger shaft, between the turbine wheel and the compressor wheel. However, this configuration presents some drawbacks. More particularly, the additional length is detrimental to rotor dynamics. The additional inertia leads to a turbolag and reduces efficiency of the turbocharger. Moreover, there are thermal limitations regarding the magnetic/electrical material (magnets or copper) fixed to the rotor, especially for a permanent magnet machine, which is sensitive to high temperature.